1. Field of the Invention
The present invention relates to a continuous fiber-reinforced Ti-based composite material and a method of manufacturing the same.
2. Description of the Related Art
Since Ti alloy exhibits excellent properties such as a high specific strength, research has been conducted in an attempt to develop mainly a space aircraft material made of a Ti alloy. In recent years, research has been directed to obtaining a Ti alloy of a further improved strength vigorous research has been made to develop a continuous fiber-reinforced metal-based composite material, hereinafter referred to as a composite material, in which a Ti alloy is allowed to contain scores of percent by volume of continuous fibers of ceramics such as SiC so as to markedly improve the strength of the composite material. The Ti alloy used for preparing the composite material is provided in many cases by a Ti(6 wt %)--Al (4 wt %)--V alloy, hereinafter referred to as Ti-64, which is excellent in, for example, the strength-ductility balance.
A hot press method is a typical method of manufacturing a composite material. In the hot press method, a metal foil used as a matrix and a reinforcing material of continuous fibers are alternately stacked one upon the other, followed by hot-pressing the stacked structure under vacuum or an inert gas atmosphere so as to manufacture a composite material. Since the hot deformation resistance of Ti-64 is rapidly increased at 800.degree. C. or less, the hot press is generally carried out about 900.degree. C. in the manufacture of a composite material using Ti-64.
The strength of a composite material is said to follow ideally the ROM (Rule Of Mixtures). In practice, however, the strength of a composite material is generally lower by at least 10% than the theoretical strength determined by the ROM. It is known in the art that the reduction of the strength is caused by a reaction layer formed and grown during the forming step at the fiber-matrix interface. The reduction of the strength is increased with the growth of the reaction layer, and the thickness of the interfacial reaction layer is increased with an increase in the heating temperature or the heating time as described in, for example, Akio Hirose et al., Zairyo (Materials), 40 , (1991) page 77.
According to the literature exemplified above, the strength of the composite material prepared by using Ti-64 and SiC continuous fibers is at most 90% of the theoretical value determined by the ROM. Since hot-pressing is carried out around 900.degree. C. in the manufacture of the composite material, it is difficult to suppress sufficiently the growth of the interfacial reaction layer in the hot-pressing step, leading to the low strength noted above.
It has been proposed to add 2% by weight of Ni to Ti-64 so as to lower the hot-pressing temperature by about 60.degree. C. and, thus, to suppress the growth of the interfacial reaction layer, i.e., to suppress reduction of the strength, as described in, for example, C. G. Rhodes et al, Metall. Trans. A, 1987, Vol. 18A, pp. 2151-56. In this case, however, the strength of the composite material is 89% of the theoretical value determined by ROM.